Spark, Adafruit, and homebrew solutions dip their toes in smart home territory.

Since Google acquired Nest for $3.2 billion last week, current and prospective smart thermostat or smoke detector owners have been apprehensive about what Google might do with the company. In the last few days, a couple of companies have stepped forward with potential open source alternatives to the service and hardware that Nest offers, sans the new implications of Google ownership.

Further Reading

The original Nest is a smart thermostat that uses motion and temperature sensors to “learn” the routines and comfortable temperature zones of its owners. It can detect when no one is home, and it normalizes to a certain temperature range over time. Users control the Nest with an app and through a Web interface.

At Spark, four engineers set to work on an open source version of a smart thermostat using their own Spark Core, an Arduino-compatible Wi-Fi development board. They added in a humidity and temperature sensor, IR motion detector, and some LEDs and LED matrices to put together and mount inside a custom wood and acrylic enclosure.

Spark kept the interface to a Web app that presents historical temperature information and has a JavaScript “knob” that allows users to set the temperature. The temperature can also be set by turning a ring on the thermostat’s enclosure.

In all, the team completed its open source version in less than 20 hours for “about $70,” including their $39 Spark Core. The thermostat is still in the experimental stage and lacks much of the sophistication and “smartness" of the Nest, but it still constitutes a networked and remotely controllable thermostat that has a memory of its own work. The Spark team posted the open source files for the thermostat on GitHub.

Adafruit, another open source hardware company, has made a platform of trying to keep data that could be produced by an “Internet of things” under control. Among its talking points are that “consumers, not companies, own the data collected by Internet of Things devices” and “users have the right to keep their data private.” The company has previously released the Tweet-a-Watt, which can be connected in series with a power strip to monitor and report the power going through it.

On Friday, the company made a blog post asking its customers if it should look into making an open source smart thermostat. The post contained only a couple renders of what a smart thermostat might look like, but several customers filled in features that Adafruit could consider to make something even more flexible than Nest’s product.

Adafruit's rendering for its proposal of an open source Nest-like product.

A number of customers suggested offering two different models: one that attaches to and controls a home’s HVAC system and a second remote sensor that would function as a display in other rooms and could communicate commands to the HVAC-connected thermostat wirelessly. Currently, Nest offers communication between Nests in different rooms, but it does not use this master/receiver model.

Commenter jorge suggested that Adafruit should include the ability to integrate an outdoor temperature sensor to “gauge the recovery period from an energy saving setback.” Most customers requested an Arduino-based thermostat, though some requested Raspberry Pi, and one responder wanted it based on the BeagleBone.

Commenter imroot at the HackerNews post for Spark’s thermostat wrote that he managed to make multiple temperature sensors using beagleboards for only $43. He controls the thermostat through a Web interface and has a Ruby script that periodically checks the temperature at the various sensor locations.

The more complicated parts of Nest’s functionality (temperature learning and effective power consumption among them) would be hard to replicate on an open source system. But remote thermostat management is turning out to be easily and cheaply attainable for interested consumers.

Casey Johnston
Casey Johnston is the former Culture Editor at Ars Technica, and now does the occasional freelance story. She graduated from Columbia University with a degree in Applied Physics. Twitter@caseyjohnston

104 Reader Comments

Make one that will operate baseboard heaters and network together so I have control over each of the four baseboard controllers as a single unit as well as zones and you'll have my money. Keeping it under $100 would make that doable for people who have a similar setup to mine... I'd gladly fork out $400 to have more granular control over each room in my home.

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

The thermostat simply sends a signal telling the attached heating or cooling unit to turn on or off. The internal electronics/controls of the attached unit determine how it runs, not the thermostat.

I want a commercially-available thermostat with remote control functionality via Android/iOS. Wifi or Ethernet connectivity is fine, but Wifi would be a necessity for most installations. I don't care about "smart" features. Nest is too costly to justify for just the remote control function.

Can you link to anything other than your own scaremongering articles as evidence of widespread apprehension about Nest and Google? I would point out that linking from your own article to your own article as evidence is pretty tacky.

Ars is really in danger of succumbing to serious echo-chamber effect. It's almost not worth visiting any more unless I want to read climate denial or Google-hating.

Maybe tone done the rhetoric a bit, jw. Arsians have been lamenting the good old days since the second article was posted. You'll live.

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

I don't think turning on and off a furnace constitutes difficulty. Maybe in your world it does but in mine, it's pretty easy to do. I don't give two red cents to any insurance company that will tell me what I can and can't buy when it comes to thermostats.

I'm not sure I care enough about Google's control of Nest to go hacking together my own "smart" thermostat. "OMG, now Google will know when I'm home!" Your smartphone already knows that. What is Google going to learn from a motion detector in your home? That you own a cat that likes to jump on tables and trigger it? That you get up to pee at 2 am on the dot every morning? Can't be bothered enough to care. This is a soft 2 on my alert scale when something breaches a 7 or higher I'll start to worry.

I looked at a Nest and thought it was majorly overpriced. Their smoke/CM detector is also very over priced. I think Google is nuts paying that kind of price for a company that makes such high end appliances. While their products show some innovation, they are beyond what the average person is going to pay for such a device.

Now come up with a home energy system that monitors the entire house, that might be something more people are interested in.

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

The thermostat simply sends a signal telling the attached heating or cooling unit to turn on or off. The internal electronics/controls of the attached unit determine how it runs, not the thermostat.

It isn't quite that simple. Temperature sensing has a bit of black magic to it. For instance, the sensors are very small and have little thermal mass. That makes them react to air flow. But you don't want a minor fluctuation to set off the thermostat. So the sensor needs to be shielded a bit. All the sensors need to be linearized. This isn't rocket science, but you do need to do a bit of research before declaring you have built a Nest clone.

I want a commercially-available thermostat with remote control functionality via Android/iOS. Wifi or Ethernet connectivity is fine, but Wifi would be a necessity for most installations. I don't care about "smart" features. Nest is too costly to justify for just the remote control function.

There are a few available - mostly based around a 'radiothermostat' design. They're sold as the Filtrete 3M50 or Homeworks CT-30. Homedepot or Lowes should have them, and I think they are around $100 (that's what I paid for mine 18 months ago.) There's apps for ios and android to let you set the temerature from anywhere with an internet connection, and you can even change the 7 day schedule remotely as well if you want.

There might be a newer version out now, I haven't checked as mine works just fine.

Not being critical or anything but can someone actually describe a convincing use case for one of these? My heating is on a timer comes on in the morning for a hour or two and bit longer in the evening. At the weekend we might switch it on for a bit longer but I don't ever find the need to change the thermostat setting. I really don't see the need to turn my heating on/off when I am not there and getting up off my arse once or twice a week doesn't strike me as a major issue either.Obviously some on here must find them useful but personally I don't really get it...

I'm not sure I care enough about Google's control of Nest to go hacking together my own "smart" thermostat. "OMG, now Google will know when I'm home!" Your smartphone already knows that. What is Google going to learn from a motion detector in your home? That you own a cat that likes to jump on tables and trigger it? That you get up to pee at 2 am on the dot every morning? Can't be bothered enough to care. This is a soft 2 on my alert scale when something breaches a 7 or higher I'll start to worry.

My phone doesn't report my presence to Google. Only the NSA and my cellular provider have this information.

I don't have an iPhone or Android phone, so I am not feeding Google wifi SSID information.

Cool stuff. There are features (or lack there of) with the Nest that make it untenable for me. Sounds like some of these open source project are going to solve those, or at least I could solve them myself. Nice.

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

The thermostat simply sends a signal telling the attached heating or cooling unit to turn on or off. The internal electronics/controls of the attached unit determine how it runs, not the thermostat.

This is not true for the majority of systems which have little to no electronic boards in the inside or outside unit. Only the higher end units will have boards that protect against short cycling.

I'm not sure I care enough about Google's control of Nest to go hacking together my own "smart" thermostat. "OMG, now Google will know when I'm home!" Your smartphone already knows that. What is Google going to learn from a motion detector in your home? That you own a cat that likes to jump on tables and trigger it? That you get up to pee at 2 am on the dot every morning? Can't be bothered enough to care. This is a soft 2 on my alert scale when something breaches a 7 or higher I'll start to worry.

I don't think people are worried specifically about Google knowing their nocturnal urinary habits.

People are worried about Google knowing that, their web search habits, their email patterns, their purchasing habits (from the scanned emails), their travel habits (via location-awareness), etc and so on.

If you have a datum about someone, it doesn't matter much. When you have data about all of someone's habits, though, it suddenly turns creepy.

Consider this: You start a garden, and order some fertilizer and such. You order a timer, some tubing, and wires to install an automatic watering system. You buy a van, because you need something to haul sporting gear around in, or kids, or whatever. You talk to your brother who's a civil contractor in Iraq.

Because you use GMail and Google Voice, Google knows that. Because the NSA are skimming data again, they see you bought most of the materials for a car bomb, and talk to someone in the middle east. Faster than you can say "But I like fresh tomatoes and ultimate frisby!", you're being investigated as a terrorist and are on a no-fly-list (not that you know it until it's too late).

(And I wish I was being melodramatic, but these days it's, IMO, all too plausible.)

There are a lot of things thermostats don't do that I'd think make sense and I would love to see more innovation:

For example, in the summer I set my AC setpoint high to save energy (maybe 78F. But If the outdoor temperature is lower than the inside temperature (in the morning or overnight), I'd like it to cool the house to as low as 70F. So setpoint = max(70, min(78F, outdoor+2F))

More complicated, if you knew the forecast from the web, you might actually save money by cooling your house more while its cooler outside in anticipation of a very hot day. Related, setting back (actually up) the AC temperature when you are at work might waste energy. Yes, your house will gain less heat overall, but moving that heat out during the warmest part of the day might be more expensive than cooling the house to a lower temperature earlier in the day (moving more heat, but more easily). A lot depends on the thermal mass of your home, but you might be able to estimate that too, and the thermostat could learn what works best.

If I have a wood stove or other space heating device, perhaps run the fan when the room to room temperature variation is above some set value.

If you have heated floors and solar hot water panels, you may want to run the hot water through the floors during some parts of the day to maximize gain, but not all day so you preserve hot water that might be needed. Again, adjust the algorithm based on weather forecast.

If you have a heat pump, knowing the outdoor temperature and the forecast would allow you to overheat your home in the day in anticipation of a cold night so as to avoid more expensive electric backup.

This all presumes one's goal is to save energy while keeping the house within acceptable bounds, but even being able to specify "ideal" and "acceptable" levels would be a big plus.

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

The thermostat simply sends a signal telling the attached heating or cooling unit to turn on or off. The internal electronics/controls of the attached unit determine how it runs, not the thermostat.

This is not true for the majority of systems which have little to no electronic boards in the inside or outside unit. Only the higher end units will have boards that protect against short cycling.

You could send the 24V signal to the unit with a paperclip for all the receiving unit cares is the point I was trying to make, irrespective of the dangers of short cycling a compressor (which can damage it, but isn't really relevant to a response about a gas heater).

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

Where's the risk at the level of the thermostat's interface with the system? I wouldn't want n00bs tinkering with the actual heater side of things; but the thermostat just turns that on or off. Will somebody end up keeping his house at something north of 90 degrees through a North Dakota winter weekend because he sucks at Arduino? Probably. Will somebody's l33t PID skills end in a few frozen pipes? Probably.

Is there a secret halt-and-catch-fire instruction in common furnaces that only the superb skill of the firmware coders for sucky bargain-basement digital thermostats has avoided unleashing? Less likely.

Plenty of room to waste energy by screwing up; but (for most houses) we are talking about something with baseline compatibility for bimetallic strip/mercury tilt-switch thermostats, not a sophisticated interface.

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

The thermostat simply sends a signal telling the attached heating or cooling unit to turn on or off. The internal electronics/controls of the attached unit determine how it runs, not the thermostat.

This is not true for the majority of systems which have little to no electronic boards in the inside or outside unit. Only the higher end units will have boards that protect against short cycling.

What is high end? In my family house we got one electronic thermostat about 15 years ago and and it has such a protection against short cycling. I guess anything that you can buy nowadays has such a basic features. I think it definitely isn't high end.

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

Where's the risk at the level of the thermostat's interface with the system? I wouldn't want n00bs tinkering with the actual heater side of things; but the thermostat just turns that on or off. Will somebody end up keeping his house at something north of 90 degrees through a North Dakota winter weekend because he sucks at Arduino? Probably. Will somebody's l33t PID skills end in a few frozen pipes? Probably.

Is there a secret halt-and-catch-fire instruction in common furnaces that only the superb skill of the firmware coders for sucky bargain-basement digital thermostats has avoided unleashing? Less likely.

Plenty of room to waste energy by screwing up; but (for most houses) we are talking about something with baseline compatibility for bimetallic strip/mercury tilt-switch thermostats, not a sophisticated interface.

I seriously considered mentioning the bimetal/mercury thermostats and decided not to. Get out of my head.

Not being critical or anything but can someone actually describe a convincing use case for one of these? My heating is on a timer comes on in the morning for a hour or two and bit longer in the evening. At the weekend we might switch it on for a bit longer but I don't ever find the need to change the thermostat setting. I really don't see the need to turn my heating on/off when I am not there and getting up off my arse once or twice a week doesn't strike me as a major issue either.Obviously some on here must find them useful but personally I don't really get it...

They anticipate when you come home; instead of just starting every day t-15m, it'll see what the prevailing conditions are like and start appropriately, for instance. Or if you have to work late or something, you can easily delay the start so you're not paying to heat or cool an empty house. On the weekend, they can sense when you're home and automatically adjust appropriately, same reason.

If you're travelling, most have a vacation mode that will automatically go into an extended temperature range. If you cut it short, or extend it, you can remotely set that.

Quite a few have fan modes, so they'll run the fans for a while before heating/cooling, which can (situationally) prevent unneeded ac/heater operation by mixing air. For instance, in my house the north end is often chilly in the summer, since the south end gets a good deal of insolation; I tend to run the fans because it reduces my bill by not firing up the AC (thermostat is in the south end of the house).

Now, if you're in an area where you just don't need to condition much, you wouldn't need one. But the temperature here just this week will range from the low 70s to the mid 20s, so we do spend a lot of time fiddling with thermostats over the year.

You know, there's a lot of complexity to running a HVAC system that I'm not sure I'd like to leave to hobbyists and DIYers... There's a ton of potential liability there as well.

I can't imagine my home owner's insurance rates if they found out I had a homemade thermostat controlling my gas furnace. I can imagine them denying my claim should the homemade thermostat cause a fire in my house...

I agree that leaving it to the DIY/hobby crowd is a bit unsettling, but for different reasons.

The bigger issue to me is making sure the thermostat heats in extremely cold conditions, which even the guys at Nest can't seem to get right. Back in late November they forced an update on all Nests (including mine) which apparently caused many of them to not charge properly, and thus stop functioning at some point in the future. This guy had all the pipes in his home freeze up on him. I lucked out- I just woke up to a 50F degree house on a night where the outside temperature was -15F. By the time I got it figured out (after a $100 service call as I was convinced my 6-month old thermostat wasn't the culprit) our house was hovering at around 38F. Nest's stance is that this only is affecting "a very small number of users" but it definitely left a bad taste in my mouth, and I'm sure the guy who had his pipes freeze is quite angry. I am looking into replacing my $250 hockey puck with a smart thermostat made by a company who comes at it from an HVAC point of view, rather than focusing on consumer electronics/juicy GUI/etc, as this kind of failure in a thermostat, brought on by a forced software update, is not acceptable.

I think this demonstrates two things: 1) there is a reasonable amount of interest in this, and 2) Google's reputation has been (perhaps rightly) sullied with respect to privacy.

Regarding the former, I have to wonder why there wasn't more interest in open source development with the launch of the original Nest? Given it's rather high price, one would think that open source tinkerers would have realized they could do it for less. None of the tech is particularly new.

As for the latter, it could be that Google is partially a victim of its own success; the public tends not to trust large corporations. However, I believe a number of its products have been sufficiently aggressive in collecting information that consumers should be wary (recent NSA shenanigans have thankfully heightened public awareness of privacy).

Not being critical or anything but can someone actually describe a convincing use case for one of these? My heating is on a timer comes on in the morning for a hour or two and bit longer in the evening. At the weekend we might switch it on for a bit longer but I don't ever find the need to change the thermostat setting. I really don't see the need to turn my heating on/off when I am not there and getting up off my arse once or twice a week doesn't strike me as a major issue either.Obviously some on here must find them useful but personally I don't really get it...

You just hit the nail on the head. Nest and other 'smart thermostats' don't really do anything for you more than a timer-based programmable thermostat. There's a little increase in convenience -- they'll develop a program for you based on your presence in the house and how you twiddle with the temperature, so you don't have to explicitly set your own program. You can see what temperature the thermostat is set to remotely, etc. Of course, with a programmable thermostat, you would know what it's set to anyway...

*PLEASE* be careful with hacking on your home heating system! Mistakes have the potential for freezing your pipes, killing your pets and plants, burning down your house, or even killing someone!

Thermostats look simple, but I designed them for a living for Honeywell and Robertshaw — a lot of effort goes into making them safe. Here are just a few concerns:

1. You need a fail-safe turn-on device (usually a mechanical bimetal switch at around 40 deg.F) to call for heat. Otherwise, your pipes can freeze if the thermostat fails.

2. You need a fail-safe turn-off device (again, often bimetal). Otherwise, it can overheat your house if the thermostat fails on.

3. Furnaces have elaborate fail-safe protection so they can’t turn on the gas flow without proving the burner has lit. They typically try to light a few times, and then “lockout” to require human intervention to check it and fix the problem. The lockout is reset by removing the call for heat, and then re-establishing it. If your thermostat does this on its own, it can DEFEAT the safety lockout, and flood your home with unignited gas!

I think this demonstrates two things: 1) there is a reasonable amount of interest in this, and 2) Google's reputation has been (perhaps rightly) sullied with respect to privacy.

Regarding the former, I have to wonder why there wasn't more interest in open source development with the launch of the original Nest? Given it's rather high price, one would think that open source tinkerers would have realized they could do it for less. None of the tech is particularly new.

As for the latter, it could be that Google is partially a victim of its own success; the public tends not to trust large corporations. However, I believe a number of its products have been sufficiently aggressive in collecting information that consumers should be wary (recent NSA shenanigans have thankfully heightened public awareness of privacy).

To me it's not so much that I worry about privacy as much as it's been made apparent that any product produced by Google can and will be discontinued at a moments notice, regardless of the number of people using it. I can live with certain things working that way, an internet connected thermostat however, not so much. If I can't rely on them for support, then I want to be able to make my own so that I know how to support it myself.

Not being critical or anything but can someone actually describe a convincing use case for one of these? My heating is on a timer comes on in the morning for a hour or two and bit longer in the evening. At the weekend we might switch it on for a bit longer but I don't ever find the need to change the thermostat setting. I really don't see the need to turn my heating on/off when I am not there and getting up off my arse once or twice a week doesn't strike me as a major issue either.Obviously some on here must find them useful but personally I don't really get it...

You just hit the nail on the head. Nest and other 'smart thermostats' don't really do anything for you more than a timer-based programmable thermostat. There's a little increase in convenience -- they'll develop a program for you based on your presence in the house and how you twiddle with the temperature, so you don't have to explicitly set your own program. You can see what temperature the thermostat is set to remotely, etc. Of course, with a programmable thermostat, you would know what it's set to anyway...

Not true at all --- consider the (very common, where I live) problem of a remote cabin in a place that can get very cold and snowbound. The ability to check the temperature from hundreds of miles away, and also to set it to be warmer in case there is a winter storm (decreasing liklihood of frozen pipes, etc, in case of a power outage) or warm up by the time I get there is very useful.

Not all temperature control is for the comfort of a present human occupant.

*PLEASE* be careful with hacking on your home heating system! Mistakes have the potential for freezing your pipes, killing your pets and plants, burning down your house, or even killing someone!

Thermostats look simple, but I designed them for a living for Honeywell and Robertshaw — a lot of effort goes into making them safe. Here are just a few concerns:

1. You need a fail-safe turn-on device (usually a mechanical bimetal switch at around 40 deg.F) to call for heat. Otherwise, your pipes can freeze if the thermostat fails.

2. You need a fail-safe turn-off device (again, often bimetal). Otherwise, it can overheat your house if the thermostat fails on.

3. Furnaces have elaborate fail-safe protection so they can’t turn on the gas flow without proving the burner has lit. They typically try to light a few times, and then “lockout” to require human intervention to check it and fix the problem. The lockout is reset by removing the call for heat, and then re-establishing it. If your thermostat does this on its own, it can DEFEAT the safety lockout, and flood your home with unignited gas!

Yeah, but this is bullshit unless you are actually mucking with the internal controls of the furnace. The standard $15 Honeywell wall thermostat you can buy at every hardware store has none of these features. It's just a crappy bimetal spring.

*PLEASE* be careful with hacking on your home heating system! Mistakes have the potential for freezing your pipes, killing your pets and plants, burning down your house, or even killing someone!

Thermostats look simple, but I designed them for a living for Honeywell and Robertshaw — a lot of effort goes into making them safe. Here are just a few concerns:

1. You need a fail-safe turn-on device (usually a mechanical bimetal switch at around 40 deg.F) to call for heat. Otherwise, your pipes can freeze if the thermostat fails.

2. You need a fail-safe turn-off device (again, often bimetal). Otherwise, it can overheat your house if the thermostat fails on.

3. Furnaces have elaborate fail-safe protection so they can’t turn on the gas flow without proving the burner has lit. They typically try to light a few times, and then “lockout” to require human intervention to check it and fix the problem. The lockout is reset by removing the call for heat, and then re-establishing it. If your thermostat does this on its own, it can DEFEAT the safety lockout, and flood your home with unignited gas!

Yeah, but this is bullshit in most cases. The standard $15 Honeywell wall thermostat you can buy at every hardware store has none of these features. It's just a crappy bimetal spring.

You'll notice that the failsafes mentioned in the quote were ---- bimetal springs?

The problem isn't that a simple thermostat is going to break, because those are run by physics. The problem is that a complex - programmed - thermostat is going to break, because it's being run by (potentially) buggy code.